turnbull

I have 2004 Pontiac Sunfire with a GM supercharger. I know it is not a Cobalt, but it is the same engine (L61), and I believe it is the same supercharger. I posted this in a Sunfire forum, but it doesn't seem like there are many Sunfire people that are knowledgeable with superchargers.

Anyway, I have a question regarding the bypass valve on the supercharger. There are 2 vacuum ports on the valve. One port has a short hose that runs directly to the supercharger. The other port is open to the atmosphere. If I am not mistaken, on the Cobalt SS, the second port is supposed to connect to some solenoid, but I do not believe this solenoid exists on the Sunfire because it didn't come with a supercharger from the factory, so it is just open to the atmosphere.

What seems weird to me is that this port is sucking in air. That means that some air is not getting filtered before entering the engine.

So my question is, is the bypass valve hooked up correctly, and if so, is it supposed to be sucking in air?

Sharkey

iTrader: (1)

yes its normal on a supercharger swapped car to have the one port on the bypass open to atmosphere. on a cobalt ss that port does go to a solenoid and the ecm uses that to limit boost in 1st gear or in an overtemp situation. its not 100% needed, in the early days people used to bypass the solenoid, but that did little if anything.

the port should not suck air through it, inside the can is a diaphragm that keeps the 2 chambers seperate, if at idle air is being sucked into the open nipple the bypass actuator is bad an needs to be replaced.

turnbull

Thanks. So how is the the bypass valve supposed to behave then? Should there be no air flow or should it be blowing air?

Also, besides unfiltered air getting into the engine, what other issues could this cause?

Crav3

iTrader: (1)

If the bypass valve is not doing its job, I would think you might be making less boost than normal at work and might have terrible gas mileage.

The vacuum line that goes to the supercharger was cracked on my car and I had bad gas mileage. After replacing it everything was back to normal. Not 100% sure just my experience

jdbaugh1

iTrader: (1)

Below is a copypasta of a comment I left on another thread explaining how the bypass actuator and bypass solenoid function.

to clarify the bypass actuator is the black diaphragm device attached to the side of the supercharger. The bypass solenoid is the device that sits up on top of the engine with wires and vacuum lines going to it. The solenoid has a boost/vacuum signal coming into the back of it from the intake manifold. It works by having a constant electrical charge sent to it which blocks the vacuum/boost signal from the manifold from proceeding onto your bypass actuator under normal conditions. If this electrical charge is either disconnected or cut off by the ECU it acts just like a flow through coupler and allows the signal from the intake manifold to place pressure on the actuator which if you are boosting will open up the bypass butterfly valve in the supercharger.You can bypass the function of the solenoid by disconnecting and plugging the line on either side of it. The only reason you have to plug it is because if you leave it open it will be a boost/vacuum leak as when the solenoid isn't energized and is open it is basically just a open line connected to your intake manifold.

Now the bypass actuator that connects to the supercharger has hose barb fittings on both the top and bottom side of the diaphragm. The top line places vacuum on the top side of the diaphragm when your throttle plate is closed off enough to create a vacuum in between the supercharger rotors and the throttle body. This prevents the supercharger from trying to boost and suck air through a closed throttle body when you aren't on the throttle hard and must stay connected. The bottom nipple works the same way but on the opposite side (bottom) of the diaphragm so that boost will push the diaphragm in the same direction as the vacuum signal (on the top side) for when the computer is telling the solenoid to pull boost or your bypass solenoid is unplugged or broken. So while you can disconnect the bottom line to prevent the solenoid from modulating boost the bottom nipple must remain open to atmosphere so it can breath and allow the vacuum signal on the top side of the diaphragm to actuate the bypass butterfly valve.

turnbull

These posts are very helpful! I did, however, already replace the bypass valve, but this would have been very useful info. I guess I should have updated this thread after I had replaced it.

I can confirm that the old bypass valve was bad. After I purchased the new valve, I compared the behavior of both valves. If I plugged one of the holes on the new valve, it made the diaphragm hard to move in and out; plugging on of the holes did not seem to affect diaphragm on the old valve.

With the new bypass valve, the bottom port is no longer sucking in air at idle. I think there might have been a slight bump in boost, but it is tough to say because the car has other problems that need to get worked out.

Lionman

Hello I been checking this thread, I'm wondering is there a setting for the bypass valve ?